1. Field of the Invention
The present invention relates to a magnetic disk controller for a zone bit recording (ZBR)-type magnetic disk.
2. Description of the Related Art
Generally, a magnetic disk unit includes one or more magnetic disks mounted on one spindle, and one read/write head is provided on each of the two surfaces of each magnetic disk. Also, the surface of the magnetic disk is divided into a plurality of tracks, i.e., concentric circles depicted by a locus of the magnetic head on the magnetic disk along the spindle. In this case, a cylinder is defined by a plurality of tracks simultaneously determined by a plurality of magnetic heads. Further, a track is divided into a plurality of sectors, a sector being a minimum unit to be accessed. One logical address, which is called an identification address (ID), is allocated to each of the sectors. In this case, an ID is defined by a head number, a cylinder number, a sector number, and the like. Thus, reading/writing operation to the magnetic disks can be carried out by indicating the head number, the cylinder number, the sector number, and the like. Also, in order to increase the storage capacity of the magnetic disks, a ZBR system has been suggested. According to the ZBR system, every surface on the magnetic disks is divided into a plurality of concentrically-shaped zones each having a different number of sectors. That is, the number of sectors is larger in an outer zone than in an inner zone, to thereby make the recording density uniform over the entire magnetic disk.
On the other hand, according to a prior art magnetic disk controller for performing a write operation of sector data in each sector, in a sector mark waiting state where a sector mark is expected to be detected, when a sector mark is detected, a write operation of sector data in a desired sector of a magnetic disk is initiated.
In the above-mentioned prior art magnetic disk controller, however, if the location of a magnetic head deviates while performing a write operation of sector data upon the desired sector, an erroneous write operation may be performed upon another sector possibly causing unexpected erasure of data therein, which will be explained later in detail.